Prior to setting forth a short discussion of the related art, it may be helpful to set forth definitions of certain terms that will be used hereinafter.
The term “MIMO” as used herein, is defined as the use of multiple antennas at both the transmitter and receiver to improve communication performance. MIMO offers significant increases in data throughput and link range without additional bandwidth or increased transmit power. It achieves this goal by spreading the transmit power over the antennas to achieve spatial multiplexing that improves the spectral efficiency (more bits per second per Hz of bandwidth) or to achieve a diversity gain that improves the link reliability (reduced fading), or increased antenna directivity.
The term “beamforming” sometimes referred to as “spatial filtering” as used herein, is a signal processing technique used in antenna arrays for directional signal transmission or reception. This is achieved by combining elements in the array in such a way that signals at particular angles experience constructive interference while others experience destructive interference. Beamforming can be used at both the transmitting and receiving ends in order to achieve spatial selectivity.
The term “beamformer” as used herein refers to RF circuitry that implements beamforming and usually includes a combiner and may further include switches, controllable phase shifters, and in some cases amplifiers.
The term “Receiving Radio Distribution Network” or “Rx RDN” or simply “RDN” as used herein is defined as a group of beamformers as set forth above.
In MIMO systems the channel is estimated by the receiver via measurements done over known patterns (e.g. transmitted Pilots); the channel estimation is used for received data decoding. While channel estimation is continuously performed by the receiver, the channel information corresponds to the combined channel and not to the individual Rx antennas. When an Rx beamformer is used and needs tuning for achieving desired weights, the channel estimation measurements are re-used by the beamformer, registering phases, amplitudes, SINRs of the various incoming signals from different antennas. Since the signals of the various antennas are combined, the assessment of each one's contribution is blurred by the others' contribution; therefore a mechanism to isolate individual contributions of each antenna is required. This mechanism has various possible implementations and is labeled “Antenna Distinguishing”.